Re: BUG #19638: Planner chooses an index-only scan for an index AM without amcanreturn, and execution fails

On Tue, 25 Aug 2026 at 00:16, PG Bug reporting form
<noreply(at)postgresql(dot)org> wrote:
> Note up front: reproducing this needs a third-party index access method, but
> the bug itself is in core, not in the extension. An AM that does not
> implement
> amcanreturn is legal per the documented index AM API; the planner
> nevertheless
> builds an index-only scan over it, and the executor then cannot run the
> plan.
> The extension is only the vehicle that exposes it -- I could not find any
> in-core AM with the required combination (see "Why no in-core reproducer"
> below), which is probably why this has gone unnoticed.

What do you mean by "required combination"? We have plenty of
IndexAMs that don't implement amcanreturn, e.g. brin.c.

Going by what you've reported in bug #19639, I'm suspecting you might
have done something to mix up the binaries for the extension.

I tried to test this, but pgvectorscale doesn't seem to support pg19:

drowley(at)amd3990x:~/pgvectorscale/pgvectorscale$ cargo pgrx install --release
Using PgConfig("pg19") and `pg_config` from
/home/drowley/pg/bin/pg_config
Building extension with features build_parallel pg19
Running command
"/home/drowley/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/cargo"
"build" "--lib" "--release" "--features" "build_parallel pg19"
"--no-default-features" "--message-format=json-render-diagnostics"
error: the package 'vectorscale' does not contain this feature: pg19
help: there are similarly named features: pg14, pg15, pg16, pg17, pg18

Did you compile it yourself? How?

David